This invention relates to the field of carbonless copy paper. Carbonless copy paper technology is an outgrowth of the historic technology in which, for instance, a sheet of paper coated with a removable carbon-containing substance was interleaved with two sheets of ordinary paper for the purpose of copying onto the second sheet of ordinary paper text or other writings as it was in the process of being inscribed on the first sheet of ordinary paper. In carbonless copy paper technology, the separate sheet of carbon-coated paper is replaced by reactive materials located on the two (or more) sheets of paper which are destined to bear the original and copied writings.
Carbonless copy paper assemblies generally employ two (or more) sheets of paper. In a two-sheet embodiment, the bottom side of the top sheet is coated with a coating that contains encapsulated dyes dissolved in oil. This surface is known as the CB (coated back) surface. The top side of the bottom sheet is coated with a coating that contains components which are reactive with respect to the dyes in the CB surface. This surface is know as the CF (coated front) surface. The CF sheet is generally manufactured by applying the appropriate coating to a paper substrate by such conventional techniques as air knife, rod, blade, and roll coating.
A typical embodiment of two-sheet carbonless copy paper is the forms that are signed in connection with credit card purchases. When the capsules are ruptured by force (e.g., the force of a ball point pen), the oils containing the reactive dyes are transferred to the CF surface and an image (e.g., of a signature) results. This technology is well known.
The dyes and oils in the capsules coated on the CB sheet are quite costly, relative to the other components of the carbonless copy paper products.
The present invention provides for improved transfer of the oils and dyes from the CB surface to the CF surface. In accordance with the present invention, the active ingredients of the CF surface are more available to the CB dyes due to improvements in the micro-structure of the CF surface. Thus, one embodiment of the present invention is a carbonless copy paper assembly comprising at least one CB sheet and one CF sheet, in which the CF sheet has a pore diameter distribution characterized by a pore diameter volume under curve of at least 0.15 mL/g.
The improvements in the micro-structure of the CF surface enable increased efficiency of the oil transfer mechanism, which means that the costly reactive components of the CF sheet can provide an acceptable level of copying at lower concentrations. In accordance with the present invention, therefore, a carbonless copy paper assembly having a desired copying efficiency can be produced more economically than comparable assemblies produced by prior art processes. Thus, another embodiment of the present invention is a carbonless copy paper assembly comprising at least one CB sheet and one CF sheet, in which the CF sheet has a color developer resin coating of less than 0.39 pounds per ream, for instance about 0.35 pounds per ream and even as low as from 0.06 to 0.22 pounds per ream.
Especially preferred color developer resins for use in the present invention are acetylated phenolic resins, salicylic acid modified phenolics, and novolac type phenolic resins.
Yet another embodiment of the present invention is a process for making a carbonless copy paper assembly. This process comprises the steps of spraying a composition containing resin capable of developing microencapsulated dyes onto paper to form a CF sheet, e.g. at a rate of about 25% solids with 4.2% resin to provide a coating of about 0.35 pounds per ream, and combining the spray-coated CF sheet with a CB sheet to form the carbonless copy paper assembly. Finally, this invention also includes the spray-coated CF sheets as made by that process.